Temporary antenna mounting on Blackhawk Helicopter
Temporary antenna mounting on Blackhawk Helicopter
(OP)
Hello,
I've been asked by some folks in the US Military to look into temporarily mounting an array of various antennae on the bottom of a Blackhawk helicopter. My company's background is in mechanical design and electronic integration. So I'm trying to find out exactly how much I don't know about mounting antennae (or any appendage) to the bottom of a helicopter or other smaller rotary wing aircraft.
The design goal is to produce a modular antenna array that mounts through and to the "hell-hole" hatch in the floor of a Blackhawk helicopter. The mechanical design of the attachment to this through-hole is straight-forward. The design of the external antennae mounts is where I'm looking for pointers. Specifically:
1. Will a low-profile, tubular structure underneath the aircraft for the various antenna to mount to be sufficient?
2. Are there specific design shapes or configurations to avoid?
3. Does anyone have experience with a similar application that might have used a different approach?
4. At what point does aerodynamic drag become a major factor?
5. Where can I go for more info on Air Worthiness Certification and what that process might incur in dollar cost to a project?
The antennae to be mounted to the base structure underneath the aircraft will be standard omni-directional antennae in both low-profile radome configuration as well as short "stick" type models. Nothing over 6-8" in length.
My basic feeling is that they shouldn't affect the aerodynamics any more than the skids of the helicopter and or other appendages to the vehicle. Operating at relatively low speeds (compared to commercial fixed-wing aircraft) seems to make the design somewhat easier. Is this the case?
Any insight would be greatly appreciated!
Thanks,
JMac
I've been asked by some folks in the US Military to look into temporarily mounting an array of various antennae on the bottom of a Blackhawk helicopter. My company's background is in mechanical design and electronic integration. So I'm trying to find out exactly how much I don't know about mounting antennae (or any appendage) to the bottom of a helicopter or other smaller rotary wing aircraft.
The design goal is to produce a modular antenna array that mounts through and to the "hell-hole" hatch in the floor of a Blackhawk helicopter. The mechanical design of the attachment to this through-hole is straight-forward. The design of the external antennae mounts is where I'm looking for pointers. Specifically:
1. Will a low-profile, tubular structure underneath the aircraft for the various antenna to mount to be sufficient?
2. Are there specific design shapes or configurations to avoid?
3. Does anyone have experience with a similar application that might have used a different approach?
4. At what point does aerodynamic drag become a major factor?
5. Where can I go for more info on Air Worthiness Certification and what that process might incur in dollar cost to a project?
The antennae to be mounted to the base structure underneath the aircraft will be standard omni-directional antennae in both low-profile radome configuration as well as short "stick" type models. Nothing over 6-8" in length.
My basic feeling is that they shouldn't affect the aerodynamics any more than the skids of the helicopter and or other appendages to the vehicle. Operating at relatively low speeds (compared to commercial fixed-wing aircraft) seems to make the design somewhat easier. Is this the case?
Any insight would be greatly appreciated!
Thanks,
JMac





RE: Temporary antenna mounting on Blackhawk Helicopter
Aerodynamic drag is unlikely to be an issue - look at the size of wheels etc.
You will need to re-stress the hatch, hinges and attachments to verify they can carry the new load in the airload, vibration and shock environment.
You say you are using omni antennas and they probably need a ground plane. I would think that the hatch surface would be evffective as a ground plane down to 600MHz and maybe 400Mhz at reduced performance. Electrical bonding the hatch for RF will be essential.
I cannot comment on attachment methods not knowing antenna needs.
and probably
RE: Temporary antenna mounting on Blackhawk Helicopter
The biggest aerodynamic issue you need to contend with is mast bending as a result of increased drag at a moment arm which can cause an effect.
What??!?!?
The rotor mast will last the predicted lifetime in configurations Sikorsky created. It could fail early if the pilot routinely flies around with the cyclic farther forward than any other aircraft as a result of the increased drag.
To determine the effect, fly to Vne clean and mark the cyclic position, you can use a tape measure to the windscreen or something. Then fly dirty to the same cyclic position, that speed is the new Vne.
Control and stability margins can be investigated too, but I would guess they aren't an issue.
Check out AC29-2C for guidance from the FAA.
RE: Temporary antenna mounting on Blackhawk Helicopter
RE: Temporary antenna mounting on Blackhawk Helicopter
Two things for you to check out:
Thread2-67807 and Forum247
this guy knows his antenna mounting stuff based on responses to questions;
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation
The requirement to mount antenna is spelled out in AC 43-13-2A Acceptable methods, techniques, and practices, Revised 1977, chapter 3. If you need a copy the AC is located on the FAA web site or contact me I will send you a copy.
Kevin
PS: As an antenna engineer, most wide beamwidth antennas like you are using are tricky and are supposed to be mounted to an official test bracket, usually a large ground plane. If you mount them just anywhere (say on something that's not a large flat surface), they may perform very poorly in some parts of the frequency band, not to mention have dropouts in the antenna coverage patterns. It's tough to VSWR test them after installation on the bottom of a helo, the ground can give false readings of poor VSWR. Good luck.